1. Field of the Invention
The present invention relates to a flow channel switching valve for use in, for example, an auto-sampler that introduces a sample to an analysis flow channel of a liquid chromatograph.
2. Description of the Related Art
As an example, in an auto-sampler that introduces a sample to an analysis flow channel of a liquid chromatograph, after the sample is taken into a sample loop from a sample container, the sample loop is connected to an upstream side of a separation column in the analysis flow channel by switching of a flow channel switching valve, which allows the sample in the sample loop to be transported to a separation column side by a mobile phase flowing in the analysis flow channel.
As the flow channel switching valve for use in the liquid chromatograph, a rotary type switching valve is common. The rotary type switching valve switches a connected flow channel by rotating a rotor (rotary part) (e.g., refer to Unexamined Japanese Patent Publication No. 2008-215494).
In the rotary type switching valve, a plurality of connection ports for connecting flow channel piping are provided in an upper portion of a housing, and a rotor and a stator (stationary part) are contained inside the housing. The rotor and the stator are in contact with each other in a state where planes thereof keep liquid tightness with each other, and the stator is fixed by a pin or the like so as not to rotate with respect to a housing side. Through-holes are provided at positions of the stator corresponding to holes of end portions of flow channels leading to the connection ports of the housing. In a surface on a stator side of the rotor, a groove communicating between end portions of the through-holes of the stator is cut, and the rotor is driven and rotated while sliding on the stator to thereby change a position of the groove and switch the connection between the connection ports.
There is also a flow channel switching valve in which the stator is integrated with the housing. It has been known that when the flow channel switching valve is used under a condition of high-pressure liquid feed, the flow channel switching valve in which the stator is integrated with the housing is higher in durability than the flow channel switching valve in which the stator and the housing are configured as separate bodies.
As a cause for decreasing the durability of the flow channel switching valve in which the stator and the housing are provided as separate bodies, in the flow channel switching valve in which the stator is provided as the separate body from the housing, a packing made of a resin is sandwiched between the stator and the housing in order to keep liquid tightness between the stator and the housing, and it is considered that this packing is inclined by influence of a liquid feed pressure.
Normally, in order to increase a contact pressure at a flow channel connecting section between the housing and the packing, a periphery of a region where the end portions of the flow channels leading to the connection ports on the housing side is depressed, and a central portion of a plane of the packing and the region where the end portions of the flow channels on the housing side come into intensive contact with each other, thereby increasing the contact pressure, and a circumferential edge portion of the packing is not in contact with an inner wall surface of the housing. Thus, if a bias occurs in the contact pressure acting on a surface of the packing from the stator side, the packing may be inclined. If the packing is inclined, a bias occurs in a contact pressure acting on a contact surface of the stator with the rotor, and a portion on which the high contact pressure acts is locally worn away.
Liquid flowing between the two connection ports connected by the groove of the rotor is guided to the groove of the rotor through the through-holes provided in the packing and the stator from the connection port on an entrance side, and is further guided from the groove of the rotor to the connection port on an exit side through the through-holes of the stator and the packing leading to the connection port on the exit side. Since an inner diameter of the through-holes provided in the stator and the packing is smaller than a width of the groove provided in the rotor, a high liquid pressure acts on the stator side from a rotor side at a portion where the liquid flows from the groove of the rotor to the through-hole of the stator. If this portion on which the high liquid pressure acts deviates from a central portion of the stator, a force that tries to incline the stator exerts, which causes a bias in the contact pressure acting on the packing from the stator, so that the packing is inclined.